This invention relates to a device for triggering a passive safety system which is installed in a vehicle and is triggered by an impact. The device has at least two acceleration sensors, the sensitivity axes of which are aligned for detecting the angle of a frontal impact. Each sensor is coupled in series with a signal channel, which comprises an evaluation circuit, particularly an integrator circuit for its output signals and a threshold value circuit.
German Patent 38 16 587 discloses a device of this type, which evaluates the signals of two acceleration sensors with cos .phi.- characteristics, mounted at an angle of +.phi. and -.phi. symmetrically with respect to the driving direction in the vehicle in its frontal area. The evaluation is performed such that collisions are detected which have a specific angle (angle .phi.) to the driving direction.
It is an object of the present invention to provide a reliable triggering device in a passive safety system which has a high adaptability to any vehicle type, particularly an expandable triggering logic which permits detection and evaluation of more characteristics than previously possible.
The principal advantages of the invention are that both the physical orientation of the signal relative to at least two aligned acceleration sensors, and the temporal development of the impact are included in the evaluation of a frontal impact, including an impact obliquely from the front within a given angle range. Thus, the triggering reliability of the detector according to the invention at a desired point in time is increased as well as the reliability in identifying only those very special types of impacts, for which triggering of the passive protection system is appropriate.
The invention also has the advantage that certain additional physical phenomena are taken into account in the evaluation of the triggering logic, which can thus identify and distinguish other disturbance factors, such as:
vehicle chassis structure (weak, flexible); PA1 breaking struts and columns in the vehicle; PA1 crumbling sheet metal of the vehicle body; PA1 knocking of the linkage on the vehicle; PA1 components that are intentionally or unintentionally movable in the case of an impact, such as bumpers, steering columns, engine block, etc. PA1 considering the impact angle; PA1 considering the channel with respect to the threshold (single channel); PA1 considering the channel with respect to the threshold and a positive g-edge (single channel); PA1 considering the channel with respect to the threshold and a positive g-edge (dual channel); PA1 considering the channel with respect to a positive and negative g-edge (single channel); PA1 recognition of preceding-sign change (single channel); and PA1 recognition of reduced acceleration signal.
Cases that are particularly critical among those mentioned, as additional acceleration causes, may lead to a faulty triggering of a safety system and thus to injuries of occupants.
The present invention also incorporate the improvements in the Applicant's German Patents 37 33 837 filed on the same date as the German Patent Document DE-PS 38 16 587, describing the spherical-symmetrical characteristics of at least two (preferably four) acceleration sensors oriented symmetrically to the longitudinal axis of the vehicle and in a plane, and the German Patent 38 16 588, filed on the same date, which discloses a triggering device with variable thresholds and a control device for the lowering and raising of this threshold; the principles disclosed in these patent documents are also in the evaluation logic of the present invention. The resulting important advantage is that the impact history, or time sequence, of the collision can be taken into account in that individual factors are linked with one another; as a result the integration constants can be changed.
Another particular advantage of this arrangement is that, by means of these individual (correction) factors, the sensitivity of the sensors can be utilized almost completely (100%) over a wider angle range-here toward 180.degree.. In other words, the triggering logic according to the invention can be utilized not only in a frontal impact direction, precisely against the driving direction, in a lateral impact, precisely 90.degree. with respect to the driving direction; and at an angle of + or -45.degree. to the driving direction, but also at all intermediate angles. By adjustment of several thresholds (-i.sub.2), it is thus possible to evaluate and recognize reliably, in the oblique impact area between 45.degree. and 90.degree. relative to the driving direction, the crash history by way of the physical signal course, with the angle recognition in the triggering logic.
Crash signal evaluation in the triggering logic according to the invention is divided into several subparts which combine to influence the physcial signal evaluation. The process includes an assessment of the "crash history" as well as of the momentary crash sequence. The instantaneous triggering time, which is a function of the forward-shifting of the driver's and front passenger's head, is determined by means of speed integrals and path integrals, as well as thresholds and reset conditions, so that a reliable triggering signal is emitted by the circuit.
The several mutually independent subparts into which the crash signal assessment is divided are as follows:
The crash direction is determined in a variable sliding time interval t, which becomes active when a crash is detected at an angle between -45.degree. and +45.degree. is measured, and remains active until either an angle outside the measuring range is determined or a period equal to 2.times.t has transpired.
The calculated values are each set back after a fulfilling of the criteria.
Only the angle determined from the relationship of the g-signals (that is, acceleration measurements expressed in gravitational equivalents; 1 g=9.8 meters/sec.sup.2) between the two sensors ml (left) and mO (right) is determined and used for the evaluation. Angle determination is performed clockwise starting from ml (right-hand system). ##EQU1## For the angle &gt;45.degree., the reciprocal value of the relationship from (1) is determined. ##EQU2## This results in a value range of: EQU 0.degree. to 45.degree.: tan .alpha.=0-1 (1) EQU 45.degree. to 90.degree.:1/ tan .alpha.=1-0 (2)
This result is used for calculation of the integration variables.
During the calculation, the braking deceleration is taken into account in order to suppress an early change of the integration variables.
The result of considering the angle with its evaluation is to increase the sensor sensitivity to approximately 100% in the case of frontal impacts which, because of the sensor arrangement, would therefore be recognized only with approximately 70% of the signal amplitude.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.